This invention relates generally to the production of kinescopes and particularly to an apparatus for thumping and airflushing kinescope panel/mask frame assemblies to reduce blocked apertures and electron gun shorts in such kinescopes.
The kinescope or picture tube for color television receivers includes a phosphor screen which is composed of alternating stripes of phosphors, each of which emits a different color of light when impacted by electrons. The phosphor stripes are produced on the faceplate panel by coating the inside surface of the panel with a slurry of one of the phosphors. A thin metal apertured shadow mask, which is supported on a sturdy metal frame, is inserted into the panel. The panel/mask frame assembly is placed upon a movable table of an exposure mechanism, commonly called a lighthouse. The lighthouse includes a bright light source which is used to expose the dried phosphor slurry to light. After the exposure is completed, the assembly is removed from the lighthouse table. The shadow mask is removed and another phosphor slurry is applied to the panel. The shadow mask is reinserted into the panel and the assembly is again placed upon the movable lighthouse table and the second applied phosphor slurry is exposed by the lighthouse. This process is repeated until all the phosphor strips are produced on the panel.
In the operation of a kinescope, an electron beam is provided for each of the three primary colors red, green and blue. The three electron beams converge at the shadow mask and pass through the apertures in the shadow mask so that each beam impacts a phosphor of the proper light emitting color. The shadow mask apertures are quite small and therefore small airborne contaminants, such as glass particles, metal flakes, dust particles, small fibers, etc. can easily block an aperture and cause a dark spot on the kinescope screen during the operation of the tube. Additionally, during the operation of the kinescope the screen and the shadow mask within the panel/frame assembly are scanned by electrons so that any particles which previously adhered to the screen or shadow mask are charged with a negative polarity. The screen and shadow mask are operated at a high positive potential so that the charged particles have a tendency to adhere the shadow mask, thereby greatly increasing the probability of blocked apertures. Also, during the production of the phosphor screen, the shadow mask is frequently inserted into and removed from the faceplate panel. This greatly increases the probability of small metal slivers falling from the shadow mask, the shadow mask support frame, and the springs and studs which retain the shadow mask in the panel. Such metal slivers can result in blocked apertures, or they can fall into the electron gun of a completed kinescope and cause electrical shorts in the electron gun. The phosphors are applied to the panels as slurries which adhere to the glass of the faceplate panel. Accordingly, airborne contaminants and metal slivers can readily adhere to the phosphors and subsequently fall from the screen and cause either a blocked aperture or an electron electron gun short. For these reasons there is a need for an apparatus for removing the maximum number of small particles from the panel/mask frame assemblies of kinescopes prior to the panels being fitted to funnels. The instant invention is directed to such an apparatus.